1. Field of the Invention
This invention relates to an X-ray generator usable as the X-ray source of an X-ray diffraction apparatus or the like, more particularly to an X-ray generator in which an X-ray beam emitted from the surface of a target bombarded with electrons is regulated beforehand within the main generator unit before passage to the exterior through an exit window.
2. Description of the Related Art
The prior-art X-ray generator produces an X-ray beam by bombarding a target with electrons emitted from an electron gun (cathode). The X-ray beam emitted from the surface of the target passes to the exterior through an exit window provided in a wall of the main generator unit.
The X-ray beam emitted from this type of X-ray generator is ordinarily regulated using an X-ray optical element to obtain a parallel beam, condensed beam, spectral or split beam or other beam with beam characteristics appropriate for the intended use.
FIG. 6 shows an example of the system layout of an X-ray diffraction apparatus utilizing this kind of X-ray generator as the X-ray source.
The X-ray diffraction apparatus has a sample base 3, a divergence slit 4, a receiving slit 5 and an X-ray detector 6 mounted on a goniometer 2. X-ray diffraction analysis is effected by directing an X-ray beam emitted from an X-ray generator 1 onto a sample S attached to the sample base 3.
An X-ray optical element 7 is provided in the path of the X-ray beam emitted from the X-ray generator 1 at a position upstream of the divergence slit 4. The X-ray optical element 7 condenses the X-ray beam emitted from the X-ray generator 1 and directs the condensed X-ray beam onto the surface of the sample S.
The peak intensities of the diffracted X-rays produced by the irradiation of the sample S with the X-ray beam appear at diffraction angles dependent on the crystal structure etc. of the sample surface. These peak intensities are detected by the X-ray detector 6. The diffraction angles (2.theta.) at which the peak intensities appear are measured by the goniometer and used to analyze the sample crystal structure and the like.
The conventional X-ray generator described in the foregoing is only capable of producing an X-ray beam by bombarding a target with electrons from an electron gun and emitting the generated X-ray beam through an exit window. It is not capable of regulating the X-ray beam generated from the surface of the target.
Such regulation has therefore required an X-ray optical element to be disposed in the open air as a separate unit from the X-ray generator.
Since the X-ray optical element disposed in the air is susceptible to contamination by moisture, dust and the like contained in the air, its X-ray beam regulation performance rapidly deteriorates.
In addition, the X-ray beam encounters resistance from air molecules. The X-ray intensity therefore attenuates with increasing length of the X-ray beam path between the window of the X-ray generator and the point of irradiation (the surface of the sample on the X-ray diffraction apparatus). In the conventional mode of use, since the X-ray optical element has to be disposed in the air between the X-ray generator and the irradiation point, the length of the X-ray path is increased at least by the size of the X-ray optical element. Wasteful attenuation of the X-ray intensity is therefore unavoidable.
Since this requires a high-intensity X-ray beam to be generated from the target in order to make up for air attenuation, it causes a proportional increase in power consumption. It is therefore uneconomical from the point of operating cost.